The Tell: The only path to a sharply higher stock market ‘is a bubble like the late 1920s and 1990s,’ says analyst who called rally off March lows

A popular stock-market valuation measure is nearing the same level it hit just before the final two years of the most powerful bull markets of the 20th century -- if it breaks out again, prepare for the building, and the eventual bursting, of another bubble, warns a Wall Street veteran who called the market's rally off the March low.